Focus: the error measure \( A-\Aex \) as function of \( \Delta t \) (recall that \( p=a\Delta t \)): $$ \begin{equation} A-\Aex = \left\lbrace\begin{array}{ll} \Oof{\Delta t^2}, & \hbox{Forward and Backward Euler},\\ \Oof{\Delta t^3}, & \hbox{Crank-Nicolson} \end{array}\right. \end{equation} $$